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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
original photogrammetric files had to be subjected to three
translations for the achievement of a presentation, suitable
for implementation with GIS system. For these mentioned
{franslations various programs are used, and most of them
provide options for the so-called translation “one-to-one”.
However these conversions may cause undesirable changes
(deviations) in the structure of the original data, and may
cause new errors. In most of the cases the errors that have
been made in the graphical elements are not discovered or
corrected in maintaining the visual contents of the map. The
customers should be acquainted with the additional errors,
caused as a result of changes in the graphical components of
editing land surveys. The errors that most often occur
consist of dislocation of graphical elements in wrong layer
or assignment of incorrect attributes [2].
With the aim of solving the above said multiple tasks a
methodology for solving problems has been developed for
the cases of incompatibility in data processing, and
particularly in case of attributes failure in the existing
outline, and of the innovation process as a whole. The end
result of the whole process for the innovation is directed to
the development of structured database that could be
formatted on the grounds of GIS database.
Preparatory Stage
The acquaintance with the exact requirements, the mapping
specifications, and the materials required are some of the
initial steps of the presented methodology. The preparatory
stage is a process of systematic and standard processes that
lay up the operator's efforts and minimise the errors in the
data analysis. At the initial check up, the whole original
database is organised in a system, and is checked for
systematic errors.
Before commencing the updating processes of the map, the
original files are converted into the corresponding software
format. Throughout the translation of the file into each
component, in addition to its original attributes, are
assigned additional attributes that provide identification of
possible corrections and changes. At this stage of
preparation, one of the qualitative control check is the so-
called representative check for co-ordinating the database of
the original survey plan.
Most of the digital graphic files or maps could be
converted from the original files into files of the
corresponding user GIS software environment. Thus, for
example the data of the individual map lists need to be
compiled into three separate files:
e DTM-file, containing broken lines and multiple
points.
e File with the contour lines.
e File containing the situational mapping
elements.
Furthermore the customer has opportunity to modify the
original files in their parts containing risk of partial loss
and/or complete failure of map data. To the present graphic
elements, a fake height value of 0 may be assigned, some
other fault height values or any data that may be
inconvenient for photogrammetric updating.
48
The contour lines with missing height values cause
displacement and deviation within the existing data for
points subjected to stercoscopic survey. This imposes the
requirement to enter correct or approximate height values
for each of the graphic elements.
One phase of the preparatory stage consists of quality
assurance techniques and possibility for optional use of the
original DTM. The analysis identifies and categorises the
graphic elements of the various groups, like for example:
e Contours without height-end.
e Contours with height-end being out-of-range.
* Contours without end but accompanied by text.
In order to implement user files which contain map data
there are files for the azimuths and master file should be
made. The supporting files that contain data have impact on
the type and the contents of each of the remaining files by
establishing and defining their variables. The maintenance
files contain the denotation colour, definition, type,
conditional signs, models, encoding text details, item
number, etc. The data are entered when the operation
environment is halted. The current print out of the new data
is an operation output that facilitates the editing process and
makes distinction between history and updated data.
The number and the situation of the milestones and
corrected points are grounded on the points, acquired as a
result of the analytical aero-photographic survey process.
The registration of new complicated model for integration
of the digital map history data could be represented in two
options [6].
Creating Digital Model of the relief
DEM is created by means of the corresponding files already
transformed. The method implements all possible and
successfully identified data, retrieved at the preparatory
stage. By means of the implemented software, the data are
transferred through various assigned actions, and analysed
in terms of compiling photogrammetrically usable files.
DTM represents the relief of the terrain with such forms as
they are in the three-dimensional (3D) space representation.
In order to represent the 3D image in GIS, both the height
and attribute of the graphical element are needed. Other
peculiarities like hydrography, type of land-use, cultures,
etc. are usually represented in two-dimensional (2D)
format. In case when necessary, by means of implementing
DEM three-dimensional representation could be added to
the two-dimensional representation of the digital map files.
The photogrammetric process of generating DEM is related
to the stereoscopic measurement of heights of terrain points
by means of analytical stereo-plotters. The point
distribution could be normal, roughly normal, or incident to
the known average density. In these observations the
network is interpolated by means of implementing means
for creating DEM. In the general case the average density of
the compiled network is 2-3 times greater than the number
of the originally measured terrain points.
